change of default text

[gauthamzz]

https://github.com/nybles/markdown-editor/blob/master/index.html#L107
has the code. it should be changed.

How to add images : Nybles logo should be displayed.
How to add links: link to nybles website homepage should be given
How to make list: list of categories available in nybles should be given
How to make Heading: Change default to something appropriate
Shortcuts should remain
Post layout should also be mentioned
Naming of articles should also be mentioned
Refer nybles.github.io readme for more details